Stairlifts typically comprise a rail following the contour of a staircase; a carriage mounted to move along the rail; and a chair mounted on the carriage, upon which the stairlift user sits during movement of the carriage along the rail. The rail of a curved stairlift will typically include bends in a vertical plane (called transition bends) and bends in a horizontal plane (called inside/outside bends). The rail may also include bends that combine vertical and horizontal elements (called helical bends).
The speed of a stairlift is limited, by regulation. Under EU regulations stairlift speed is limited to a maximum of 0.15 m/s but this limit may vary in other jurisdictions. The reference point at which speed is measured is a point on the surface of the stairlift chair, at a position forward of the rear edge.
In the case of curved stairlifts, when the carriage is moving through a negative transition bend (a bend in which the angle of inclination reduces in the uphill direction) the speed of the reference point on the chair will accelerate relative to the carriage. Similarly, as will be described in greater detail below, when the carriage is moving through certain types of inside/outside bend, the reference point on the chair will typically proscribe a greater arc than the arc through which the carriage is moving and, accordingly, the reference point will accelerate relative to the carriage.
To ensure that the speed at the reference point does not exceed the prescribed upper limit, the stairlift carriage is typically slowed as it moves through bends. The changes of speed may be effected by placing switches along the rail, each switch serving to trigger a speed change in the carriage as the carriage moves past the switch. One alternative is to ‘map’ the rail in the broad manner described in our European Patent 0 738 232. In this case, the positions on the rail at which the carriage should be slowed or accelerated, are stored in an electronic memory. The position of the carriage on the rail is then monitored and the carriage speed then adjusted to that which is appropriate for the position on the rail.
Further factors may influence the speed of a stairlift, two being battery voltage and motor current draw. These are typically limited, empirically, to avoid damaging the batteries, it being recognized that demand on the batteries will vary according to factors such as passenger weight, carriage speed, initial state of charge of the battery, whether the carriage is moving up the rail or down the rail, and whether the carriage is moving through a transition bend necessitating operation of a levelling motor to maintain the chair level.
In order to accommodate these various factors, the speed of the stairlift is set somewhat arbitrarily, and based on experience, to ensure not only that the maximum permissible speed is not exceeded but also that battery voltage and current draw are maintained within limits. Invariably this means that the total time taken for the carriage to travel between the ends of the rail is longer than is necessary, and than is possible.
It is an object of the present invention to provide a method of controlling the speed of a stairlift, and/or a stairlift so controlled, which goes at least some way to addressing the problems identified above; or which at least offers a novel and useful choice.